The insertion unit of an endoscope is equipped with a treatment tool channel through which a treatment tool is to be inserted. Not only is an observation part observed using an image sensor that is installed in a tip portion of the insertion portion, but also the observation part may be treated using a treatment tool that is inserted through the treatment tool channel.
An example treatment tool is a radio-frequency treatment tool such as an electric scalpel. JP-A-2011-212161 discloses an endoscope in which a shield piece is disposed so as to be continuous with a circuit board to which an image sensor is connected and exposed conductor portions of cables that are connected to the circuit board are covered with the shield piece. This measure suppresses mixing, into input and output signals of the image sensor, of noise that is radiated from a radio-frequency treatment tool.